Die mechanism accelerators for flying cutoffs are well known. Hydraulic and pneumatic accelerators are typically very complex, bulky, and expensive devices and represent a limiting factor in the reliability of a flying cutoff system. Mechanical accelerators utilizing racks and pinions are also known and, in fact, may be preferred in some applications because of the accuracy with which the position of the die mechanism may be determined from pinion rotation. Mechanical accelerators are also very expensive due to the precision machining requirements and length of the rack. They are also bulky since the rack can be very long and requires a cover of even greater length to stand adjacent the cutoff press.
Linear actuators using rotating shafts and travelers are also known. A threaded shaft, for example, may be driven by a reversible motor to cause linear translation of a "trapped" nut which is mounted on the shaft. The nut may be connected, for example, to a garage door to move the door between opened and closed positions.
A difficulty with mechanical actuators such as the rack and pinion and screw-shaft types described above arises out of the unforgiving nature of the connection betwen the power source and the driven load; i.e., the direct and positive mechanical connection which produces the desirable quality of position-predictability can give rise to calamitous results if an obstruction is encountered by the driven load due to a malfunction in some other area.
Linear actuators using non-threaded shafts are also known. Such devices use a smooth shaft connected to a motor, and a traveler comprising several rollers the axes of which are skewed relative to the shaft axis so that rotation of the shaft causes the traveler to move longitudinally along the shaft. Such devices are generally considered unsuitable for precision applications since the pressure-dependent nature of the roller-shaft contact can give rise to slip under high load conditions.